Improve tests for container-name autocompletion for exec commands

[TessaIO]

What would you like to be added?

Tests in container-name autocompletion are done in separate functions and they don't cover the actual functionality which is auto-completing the container-name. We can compact those methods in a test table and add more tests to cover more cases.

Why is this needed?

This is needed to improve the confidence in these tests and make them more maintainable and clean.

[k8s-ci-robot]

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[TessaIO]

/assign

[TessaIO]

/sig cli

[TessaIO]

/transfer kubectl